It is well known that nucleators (often used in conjunction with supplementary amine "boosters") can be used in photographic materials to provide very high contrast images useful for graphic arts applications. The level of nucleation activity achieved in a material can be modified and the established art is to control the nucleation process by, for example, adjusting the level of, and/or the type of nucleator, in isolation, or in concert with similar kinds of changes to the booster. This is a crude, time-consuming method demanding the development and synthesis of new nucleators and boosters, whereas varying the nucleator level provides only a very limited level of control.
It is important to control the level of nucleation activity not only to ensure high photographic contrast, but also to control the level of "pepper" fog, that is, the number of undesirable black spots in otherwise clear image areas. Also, it is important to control the level of nucleation activity in order to control the rawstock keeping stability of the material.
U.S. Pat. No. 5,512,415 describes a high contrast photographic material comprising a support bearing at least one silver halide emulsion layer wherein the photographic material contains a hydrazine nucleating agent and a polymer latex having a core/shell structure wherein each are incorporated in at least one of the silver halide emulsion layers and other hydrophilic colloid layers of the photographic material. The polymer latex is added to improve the physical properties of the photographic material, e.g., wet film strength or scratch resistance.
A much more refined method of nucleation control is required, allowing the level of pepper fog and raw stock keeping to be controlled to provide the desired product performance.